Starting and regulating apparatus for free-piston compressors



E. A. wAcHsMuTH 2,841,322 STARTING AND REGULATTNG APPARATUS FOR FREE-PIsToN coMPREssoRs 4 Sheets-Sheet 1 July 1, 1958 OriginalIFiled May q.. 1952 E. A. WACHSMUTH STARTING AND REGULATING APPARATUS July 1, 1958 FOR FREE-PISTON COMPRESSORS Original Filed Hay 1.**1952 4. Sheets--Sheet- 2 www@ July 1, 1958 E. A. wAcHsMuTH 2,841,322

STARTING AND REGULATING APPARATUS FOR FREE-PISTON COMPRESSORS *original Filed may 1. 1952 4 sheets-sheet s f f f4 (F5 af 7 76 ya //...lv l.

July 1953 E. A. wAcHsMuTH 2,841,322

STARTING AND REGULATING APPARATUS FOR FREE-PISTON COMPRESSORS 4 Sheets-Sheet 4 Original Filed May l. 1952 M @Wwwj United States Patent @hice dig Patented July l, 1958 STARTING AND REGULATENG APPARATUS EUR FREE-PESTQN CR/PRESSRS Erich A. Wachsinuth, Michigan City, ind.

Continuation of application Serial No. 255,472, May l, 1952. This application January 2, 1957, Serial No. 634,395

4 Claims. (Cl. 23S-m52) This invention relates to free-piston internal combustion engine-driven compressors, and more particularly to starting and regulating apparatus for such compressors.

Free-piston machines of the character referred to are usually started by compressed air. The engine-compresser piston pairs are moved to the outer ends of their strokes and locked in what may be called starting position. They are then subjected to the pressure of an eXpansible fluid under pressure tending to force them together, and when that pressure is at the requisite level for starting, the pistons are released and driven towards each other by the expansion of the expansible lluid, and the air trapped between the motor pistons is compressed to such aV degree that fuel injected into the motor cylinder in the neighborhood of the dead center is ignited, and the explosion drives the pistons apart again. By the end of this rst stroke, there must, independent of the pressure in the receiver to which the compressor may be discharging (for that pressure might be low), be energy stored up suiiicient to return the piston pairs to their inner positions and to compress the air between the engine pistons to the requisite degree. This is accomplished in various Ways, as by interposing a pressure-maintaining valve between the discharge valves of the compressor and the receiver, thus causing the compressor, regardless of the prevailing receiver pressure, to Work against a pressure In my copending application, Serial No. 272,019, liled February 18, 1952, now Patent No. 2,775,398 for Free- Piston Compressor, a quite diierent starting arrangement is employed. There a twin unit is started by the explosion of a suitable powder charge producing a pressure acting between the motor pistons of one pair to force apart the piston pairs of which such motor pistons form a part. According to that arrangement, the pistons in the starting cylinder (the motor lcylinder in which the eX- plosion to eect starting is to take place) are brought close to each otherinto their innerdead center positions, and driven apart by the ignition of a predetermined powder charge. Thereupon, through the coupling of the pistons which characterizes this design, a driving together of the piston pairs of the other cylinder takes place, and the air between the motor pistons of these latter pairs is compressed, and fuel injected near the dead center point of this latter cylinder is ignited, and the pistons of this cylinder are driven apart While compression is again effected in the first cylinder. The machine of application Serial No. 272,019, now Patent No. 2,775,398 also needs pressure-maintaining valves or buier cylinders, but its need for them, in contrast with the free-piston machines lirst described (which would not otherwise make a second stroke) is to prevent the machine from running away.

The general object of the present invention is to provide, without the necessity for pressure-maintaining valves or special buler cylinders (which are undesirable both from the operating and the cost standpoint), an improved apparatus for the satisfactory and simplified starting of twin free-piston machines. Another object is to provide an improved starting and controlling apparatus for freepiston compress-ors of the type mentioned. A further object is to provide an improved method for the starting and control of free-piston machines. Still another object is to provide an improved controlling device for governing a free-piston machine while receiver pressure is below the lower designed working limit and, in association therewith, improved means automatically controlled while receiver pressure is between the relatively closely spaced upper and lower limits of the designed pressure range for controlling the air delivery of the machine and governing the fuel supply so that it s properly related to the air delivered. Yet a further object is to provide an improved controlling device for governing a free-piston machine including two pressure responsive control devices, the first, in control while the delivery pressure of the compressor is below the lower limit of the designed pressure range, acting to control the fuel suppy to the motor, increasing it as the pressure against which the compressor discharges increases, and the other, in control while the compressor is delivering air at pressures between the upper and lower limits of its designed range, controlling the quantity or' air delivered to maintain the receiver pressure within the desired range and taking over the control of the fuel supply to the motor and controlling the supply so as to maintain the power output and the Work done by the cornpressor in balance. Other objects and advantages or the invention from its various aspects will hereinafter appear.

According to the invention, after the ignition of the powder starts the machine, and up to the time the lower limit of the designed pressure range of the compressor is reached, the quantity of fuel injected is automatically regulated t-o keep step with the continuously incre? work required for the compression of air to the pr sively increasing discharge pressure and its discharge against such increasing pressure, but, as the receiver pressure varies in the range between the lower limit of the dcsigned range and theupper designed limit, the quantity of compressed air discharged per stroke is varied while there is effected a concurrent change in the quantity of iniected fuel quantity decreasing, between the lower and upper limits of the designed normal pressure range, from a quantity suited to full load operation to one suited to no load operation.

A very desirable embodiment of the apparatus aspect of the invention includes a pressure responsive device (a starting pressure responsive device) engaging, indirectly or directly a suitable transmission elementa two-armed lever is appropriata-and acting through the latter t the regulating element of the fuel pump, in such a as to elect an increase in the quantity of fuel dmv e with an increase in the pressure to which said pr responsive device is subjected, the operating ran this mechanism lying between absolute atmcs pressure (substantially zero gauge) and the lower of the designed operating range. This embod. mi t further includes a second pressure responsive device (an -operating one), which is effective between the lower and upper limits of the designed pressure range of the apparatus-that is, within the normal operating rangeand which acts, indirectly or directly, on the free end of the two-armed lever in such a manner that the quantity of fuel injected is diminished with increases in the pressure to which the second pressure responsive assises ordinated with receiver pressure in such a manner that when receiver pressure is one atmosphere gauge there is supplied the proper quantity of fuel to be -burned to effect the compression and discharge of the quantity of air taken in, and when receiver pressure is two atmospheres gauge, the quantity of fuel injected is modified to provide the worlr involved in delivering 'against a pressure two atmospheres the air taken in, etc.

A systematic calculation, on the assumption of normal partial load eticiencies of the motor and on the basis of output increments measured on single stage compressors, demonstrated that between one and eight atmospheres receiver pressure (roughly zero and 103 pounds gauge), the amount of fuel required to be injected increased linearly with the air pressure. Accordingly, when a closed fuel pressure system is used, it should be possible to use a fuel pump with a helix-shaped control edge in a system such as is diagrammatically shown in Fig. 4, with the angle of inclination of the helix determined from the maximum useful stroke, the maximum and minimum delivery, and the fuel pump plunger displacement angle (degrees of rotation on its axis) between full load and no load. eviations resulting in actual practice'between the delivery law of the plunger thus determined, for example, of the pump and the actual fuel requirement may be taken care of by the insertion of a variable displacement device 68 to correct the movement of the regulating rod as shown in Fig. 4. The pressure responsive device 4i maintains control of the fuel injection pump between zero (standard atmospheric pressure at sea level) pressure and the pressure which is selected in the design of the Aapparatus as the lower limit of the desired normal operating range, and as the design features which have been described are generally well-known in the internal combustion engine art, it is unnecessary to illustrate any of the details of construction of the fuel pump. It may be said, however, that there may be employed any suitable conventional fuel pumps, including pumps similar to the hydraulic impulse givers later described, such pumps having cam-actuated plungers provided with generally helically disposed surfaces and rotatable on their axes to vary the fuel delivered, said surfaces, through their uncovering or covering, according to their disposition on the plungers, of a lateral port extending between the pump cylinder bore and a fuel supply space, determining the end or the beginning of fuel delivery. These pumps may, for example, be actuated from the shaft 9; and, if fuel injection during any portions of the working strokes were desired, accumulators might be provided as needed.

Another pressure responsive device, responsive to receiver pressure, is shown at 43 and this controls a device 42 for controlling the quantity of air delivered, and this pressure responsive device 43 becomes operative as a control as soon as receiver pressure exceeds the normal lower limit of the operating range, for example seven atmospheres gauge, Within the normal operating range from, say, 7 atmospheres gauge to 7.7 atmospheres gauge, the device 42 adjusts the amount of air delivered by the compressor from maximum all the way down to zero delivery. ln accordance with the two compressor systems operating in counterstroke relation, device 42 consists of two congruent units which, like the fuel pumps, are suitably arranged in opposed relation and are driven in opposite directions by the symmetrical anks of a cam located on a free shaft end (herein an end of shaft tl) of the rocker whose shaft does not actuate the fuel pump. As in the case of the fuel pump, the control element of each unit is a plunger with a sloping control edge reciprocated in rhythm with the motor-compresser piston with which it is coordinated and moving in a bore in a cylinder which is provided for it. The

shape of the control edge is determined empirically, in connection with the mechanical coupling for the control rod of the fuel pump, so that for each load stage of the compressor the work output of the motor and the work absorbed by the compressor are in equilibrium.

During each reciprocation of its piston the control device 42 produces in a well-known manner pressure irnpulses which are used to control claws or fingers cooperating withthe compressor suction (inlet) valves in such a way that the suction valves are held open for a smaller or larger portion of the compression strokes. Each of these control units acts simultaneously on two claw or finger systems, one associated with each of the alined compressor cylinders of a pair.

Two different control arrangements for maintaining the inlet valves open for the desired portions of the cornpression strokes of the compressor pistons are shown respectively in Figs. 5 and 6. In the arrangement of Fig. 5 the control unit consists of an edge-controlled pump with suction valve 46, but without discharge valve. rl`he figure shows the controlling piston or plunger 51 in its lower dead position. With respect to the compressor, this position corresponds to the dead position preceding the `compression stroke, in other words the positions occupied by the pistons in the compressor cylinders 3T., 33 in Fig. l of the drawings. It will be understood that, since, when a reciprocating element reverses its motion, it is stationary for an instant between its opposite strokes, it has a dead position or dead point, and indeed such dead positions and dead points occur at each o-f the opposite ends of the paths of reciprocation. Commonly the dead points and dead positions are known as dead center positions when the reciprocating element is connected by a connecting rod with a crank, and it is believed no unwarranted extension of usage of the term dead center to apply it to a free-piston type of machine to indicate the ends of rthe piston strokes.

When the piston or plunger Si goes up, immediately the pressure medium (e. g. oil) lling the space d3 is pushed out, against the spring force opposing movement of the claws or fingers 60, into the cylinders 6i, until the clawor finger-operating pistons 62 are stopped by the abutment 63. Thereafter the pressure medium displaced by the plunger is blown olf through a closed fuel injecting nozzle itl connected back to the fluid supply and acting as a safety valve Whose relief pressure is higher than the pressure reached in the system at the moment the claw-operating piston is stopped by its abutment. As the oblique edge S moves (upwards in Fig. 5) over the control port 52, the pressure in the system is relieved, and the claw spring 64 pushes the claw piston 62 and claws back into the inoperative position with high acceleration. At this instant only can the compressor suction valve close and the compression begin (see diagram of Fig. 8). The control piston or plunger S1, continuing its upward movement, now expels the pressure medium from the space S3 above the piston through the laterally vented central bore 5d in the piston and the control port 52 into the space 55, which communicates with the suction space 57 through the throttle gap 55. When the plunger Si moves down, the suction valve 46 opens, so that pressure medium can flow from the suction space 57 into the developing space 53, during the entire downward movement of the piston, and an evacuation of the system, with vacuum formation, is reliably prevented.

The pressure impulses produced by the above described control arrangement give a control which is not symmetrical with respect to the dead position. The fact that delivery of pressure medium, which here sets in positively only with the piston reversal of the motorcompressor (see Fig. S) is the reason the control impulse arrives at the claws a little (though only a little) after the piston reversal and why the claws start to move in a direction to maintain the compressor suction valves open only after the compression stroke has set in, geometrically speaking. in View of the fact that suction valves, as a result of their inertia, close late too, this retardation will as a practical becajtis'ethe claw movement occurs symmetricall dead point, that is, it sets in 'at any rate before Ythe dead be noted. With fundamentally the same arrangement as Y in Fig.` 5, but with modified control cam position, mcdilied plunger T. with modified control edge S', and with replacement of the safety valve 7i) (Fig. 5), by a preloaded pressuremedium accumulator 84), acontrol operating symmetrically with respect to theV dead'poiitr can be effected (seeFig. 9). Vit is Valso possible to do without the suction valve 46 of Fig. 5.

The outward` movement ofV the piston Slris coordinated in this arrangel V:ajenas/afa Y control-edges and. to'theA control-edges ofvk the device. Y42 controlling theV quantity of Vair delivered.

'ln detail: 4l representsthe 'pressure responsive deviceV Y 35. 86 represents the point ofpivotalconnectionof the l p' piston rod 84 with a'tWo-armed lever S7, which is connected; on .the onehand, with Vthe *regulating-'rack R of the fuel pump?, and,.on the other hand, at the articu- 1 nlation point 93, with the displacing element (regulating ment witb'the suction stroke of `the compressor. 'in

other words, the upward movement or during the suction, Strokes of the compressor pistons,

and not, as in Fig. 5, during/'their discharge stroi The oblique control edge S of the piston 5l determines thebeginning of delivery. The upwardly moving piston at i'irst VVforces thecontrol medium trom space S3 back into the suction space 5.7. When the control port 52 is coveredearlier or later dependingY on the amount of Y plunger rotation-by the slanting edge S', fluid delivery commencesk and the claw-operating piston is displaced against spring force' in the keep open direction at a velocity which corresponds to the reduced plunger velocity. After Ythe claw-operating piston 62 `is stopped by abutment e3, the control rnediurn delivered is stored by the pressure medium storage tank or accumulator Deiivery and storage continue until reversal ofthe plunger 5i. Upon reversal, the system remains under the storage pressure until the accumulator' Sil is empty. Only then ,does the claw piston 62,v go baci; under the pressure ot the spring 64 iacting on it.Y ItV reaches its inoperative. position at the moment the control edgeS reopens theV controlrport 52. The plunger 51 itself continues to move Y' while'the space 53 being created by its movement fills Yup-irom the suction space E? until the'lowerV dead position isreached. L .Y v

VThe arrangement of Fi. 6 ensures acorrectly timed control also in the partial load range close to full load, tothe point. The relatively slow return of the claw piston' be compensated for by a corresponding setting oL the iustant'of control. This arrangement presupposes atlglrt Vpressure rmedium storage system for the claw control.

Leakages would displace the instant of clawY return toward fullV load..A Since as to fuel supply no correction 1n Y 'the same sense takes place, major system leaks would disturb the equilibrium between motor and compressor and the machine would come to a standstill. Y Y

in each of the arrangements Vof Figs. 5 and 6 the hydraulic impulse givers' have their plungers actuated as shown by cams 10i) (Fig. 5) and 100 (Fig. 6) mounted on the rockershaft S, but by reason of the different dispositions of the cams and the different formations of tbe Yplnngers 5l and 5l',Y projection ofthe claws'or fingers commences immediatelyV after the commencement of theY compression strokes of the compressor Ypistons in the arn rangementof Fig. Y5,'hutY commences in 5 after the 'be' employed in 'eitherpof' the schematically shown Yarf rangements of Pigs. 3 and 4. Y f A According to VschematicY Fig. 3 the adjustment oi theV charge ofV Y sure), and

fuel supply to the work of compression anddi the air (which is dependentY on the receiver pr of the quantityrof airto be handled to the fuel supplied, Y fare obtained by giving a suitable orm tothe fuel-pump this plunger occurs vice (operating box) d3. acting overrthe pressure range between the lower Vand the upper designed operating pres-Y sures consists ofV the cylinder 94%,. the piston'e' with its pistonV rod 96 and, the spring 97 suitably tensioned to;

causeit to commence to yield only when the lower rated 1 vices) 41 and 4?;` with the receiver (not shown in Fig. 3). j

it will be understood'that with twin pumps and twin hydraulic impulse givers the `elements R and R willrbe duplicated and those o'f'each pair'will be Vconcurrently actuated. .7 Fig. 4 shows fundamentally the same arrangement, a1- though under the employment of a normal fuelY pump, that is, a pump with a linearV control-edge pitch. In thisY the regulating-control-rod path and the receiver pressureY f canne longer be truly proportional. with Veach other. Here the transmission ofY the action of the pressure boxV lll to the regulating rod R of the fuel pump VtakesV place through an Vinterposed'motion adjusting plate- 45S, which, on being rotated, as byV a rack and pinion transmission' 9i, by the piston 83 of the pressure boxV di', controls the displacement of the'.positively-connected ,motion'adjustfV ing plate 63, and this determines the path ot Vthe rod 84. l Note plate 68 controls'positioninbothdireetionsfiY Y VTlThe-rnetliod of Yoperation of thearrangements ofFigs. 3V and 4 is, 'furthe rest, exactly alikef s i f TheV illustrations correspond. to the `conditions'present 'I beforeV starting oithecompres'sor. Y With rising receiver pressure the pistonsfSS move, ,against the pressure ofthe n springs Se', towardzthefright, While theY pistons 95, owing 'Y to a high spring tension, remain Vatiirst at rest. `The Y pistons @3, moving toward therightdisplac'e, through the lever S7 swinging'aboutV the stationaryy point t), the regui lating rodR, in accordance'with the increasing'work of,`

compression, toward full load, which is reachedV at the"` Y endipositionof thejpistonsV 63, corresponding to the lowen limit ofV therde'signed Vnormal pressure Vrange. Asthe pressurecontinuesto ,rise further, theY pistons corniVVV mence to move toward the right, and to'displace, through the adjusting element Rf, Whichlis `also moving :towardV Vthe right, that is, in the *direction*of.zerojdeliveryfandf. y

inecessary for motor piston return rand the'work of cornpression-Work can be stored in the buffer cylinder without the help of the compressor cylinder.

In conclusion, the diagrams of Figs. 8 and 9 may be noted briey. These may be regarded as illustrative of the use of the inlet valve controls of Figs. and 6 respectively. In Fig. 8, it will be noted that the inlet valve opens at the end of the reexpansion of the air in the clearance spaces of the compressor and remains open throughout the rest of the suction stroke. They start to reseat at the end of the suction stroke, but are held open for a part of the discharge stroke by the claws or lingers, which are actuated right after the compression stroke commences, and are held in valve opening position until the edge S overruns the port 52 and lets the pressure acting on the plunger 62 bleed down.

In Fig. 6, the cam 100 commences to move the plunger 51 at the beginning of the suction stroke, but no uid is displaced which moves the plungers 62 until the edge S closes the port 52. This, as illustrated in Fig. 9, occurs at about 3/s stroke, but it may obviously occur later or earlier dependent on the rotation oi the plunger 51'. The claws then move out and at the end of the suction stroke will prevent the closure of the inlet valves which had been opened and were held open by suction. During the discharge stroke the plunger 51' will be permitted to move down and uncover the port S2, the inlet valves will close, and compression of iluid will commence, the amount discharged depending on how late in the discharge stroke the inlet valves are held open.

This application is a continuation of my copending application Serial No. 285,472, tiled May 1, 1952 now abandoned.

While there are in this application specifically described two forms and certain modications which the invention may assume in practice, it will be understood that these are shown for purposes of illustration, and that the invention may be modified and embodied in various other forms without departing from its spirit or the scope of the appended claims.

What I claim is:

1. In an apparatus for varying the quantity of liuid delivered per stroke by a compressor which includes a reciprocable piston, a cylinder for said piston, said cylinder and piston coacting to form a chamber in which compression of a fluid is effected by relative movement between said cylinder and piston, said cylinder having an inlet valve, a shaft and a connection between said shaft and piston such that they move in given relation to each other, in combination, hydraulically operable expansible chamber mechanism for holding the inlet valve open through a portion ofthe compression stroke of the piston, a hydraulic impulse giver having means for varying the period during which it displaces fluid, means driven by said shaft for causing said impulse giver to start to deliver its impulse with the compression stroke of said piston, conduit means connecting said impulse giver with said hydraulically operable expansible chamber mechanism whereby impulses delivered by the former control the operation of the latter, and means governed by compressor discharge pressure controlling said hydraulic impulse giver to adjust the period during which the eX- pansible chamber mechanism is subject to the impulse.

2. In an apparatus for varying the quantity of uid delivered per stroke by a compressor which includes a reciprocable piston, a cylinder for said piston, said cylinder and piston coacting to form a chamber in which compression of a liuid is ettected by relative movement between said cylinder and piston, said cylinder having an inlet valve, a shaft and a connection between said shaft and piston such that they move together, in combination, hydraulically operable expansible chamber mechanism for holding the inlet valve open through a portion of the compression stroke of the piston, a hydraulic impulse giver having a plunger initiating an impulse upon attaining a given position and having means for varying the period during which it delivers its impulse, means turning with said shaft for causing said impulse giver to start to deliver its impulse with the compression stroke of said piston, conduit means connecting said impulse giver with said hydraulically operable expansible chamber mechanisrn whereby impulses delivered by the former control the operation of the latter, and means governed by cornpressor discharge pressure for adjusting said means for varying the period of delivery of the impulse by said impulse giver to vary such period.

3. In an apparatus i'or varying the quantity of uid delivered per stroke by a compressor which includes a reciprocable piston, a cylinder for said piston, said cylinder and piston coacting to form a chamber in which compression of a fluid is effected by relative movement between said cylinder and piston, said cylinder having an inlet valve, a shaft and a connection between said shaft and piston such that they move in given relation to each other, in combination, hydraulically operable expansible chamber mechanism for holding the inlet valve open through a portion of the compression stroke of the piston, a hydraulic impulse giver having a reciprocable plunger and means for varying the duration, from a constant point in its stroke, of its displacement of iiuid, means for initiating plunger movement at the commencement of the compression stroke ot said piston, means connecting said impulse giver with said hydraulically operable expansible chamber mechanism whereby impulses delivered by the former control the operation of the latter, and means governed by compressor discharge pressure for adjusting said duration-varying means for varying the period of delivery of the impulse by said impulse giver.

4. In an apparatus for varying the quantity of lluid delivered per stroke by a compressor which includes a reciprocable piston, a cylinder for said piston, said cylinder and piston coacting to form a chamber in which compression of a fluid is effected by relative movement between said cylinder and piston, said cylinder having an inlet valve, a shaft and a connection between said shaft and piston such that they move in synchronisrn, in combination, hydraulically operable expansible chamber mechanism for holding the inlet valve open through a portion of the compression stroke of the piston, a hydraulic impulse giver having means for varying the period during which it displaces tluid, means driven by said shaft for causing said impulse giver to deliver its impulse during the compression stroke of said piston, conduit means connecting said impulse giver with said hydraulically operable expansible chamber mechanism whereby irnpulses delivered by the former control the operation of the latter, and means governed by compressor discharge pressure for adjusting said means for varying the period of liuid displacement by said impulse giver to vary such period.

No references cited. 

